This isn't for the inexperienced.

You are receiving video at one frequency, digitising it, then outputing it at a different frequency depending on your video resolution.

A PIC alone does NOT have the capability to handle this. You need a LOT of additional supporting hardware.

You will spend countless hours and many 100's of $ to achieve this... when it has been done already... do a google search for GRANDTEC VGC1000 for about $50...

Doing it yourself will probably take AT LEAST a couple of months of your life, some expensive test equipment, and probably a minimum of $250...

May I respectfully suggest you pick a simpler project.